Thin magnetic films deposited (e.g., by physical-vapor deposition processes such as plasma sputtering and ion-beam deposition methods) onto substrates in low-pressure processing environments can be magnetically oriented to a single axis, a condition referred to as xe2x80x9cuniaxial anisotropyxe2x80x9d, by exposing the films to orienting magnetic fields with sufficient field strength that exhibit high magnetic flux uniformity and little angular skew during the deposition or subsequent post-deposition processing of the films (such as magnetic annealing processes). Magnetic orientation of thin films can take place in conjunction with various applications including thin film deposition and thermal anneal processes as well as thin-film magnetic metrology.
Thin-film magnetic recording heads are usually fabricated using a combination of material layers including one or more layers of thin soft and hard magnetic films, some of which may have magnetic domains oriented along one or multiple magnetic axes. Generally, the magnetic films are deposited onto substrates in low-pressure processing chambers by physical-vapor deposition (PVD) methods such as plasma sputtering or ion-beam deposition processes. The magnetic domains of these films are oriented by exposing the films to in-plane magnetic fields either during their deposition or during a subsequent processing step such as magnetic annealing. The magnetic fields have specific requirements specifying the upper limits for both xe2x80x9cskewxe2x80x9d (deviation in direction) and xe2x80x9cnon-uniformityxe2x80x9d (deviation in magnitude). Typical in-plane magnetic field strengths are in the range of 50 to 100 Oersted.
Either permanent magnets or electromagnets can be used for generating the substantially uniaxial magnetic fields. For example, Nakagawa et al. in U.S. Pat. No. 4,865,709 mount thin magnetic film substrates between pairs of permanent magnets on a substrate holder. Opposite poles of the magnets face each other for generating approximately uniaxial magnetic fields across the thin film surfaces of the substrates. However, the permanent magnets are difficult to position, have limited magnetic field strength and adjustability, and are exposed to processing that can affect their long-term performance (resulting, for instance, in long-term field drift). Permanent magnets may also have detrimental effects on the PVD plasma uniformity and repeatability. Moreover, permanent magnets provide no or limited capability for field magnitude or orientation adjustments.
Setoyama et al. in U.S. Pat. No. 4,673,482 position a pair of magnetic field-generating coils on opposite sides of a substrate outside a low-pressure processing chamber in which the substrate is mounted. The coils are located at a considerable distance from the substrate and only a small portion of the resulting magnetic field exhibits the required uniaxial characteristics. Magnetic field adjustability is also limited. Moreover, this type of magnetic field source can produce significant plasma non-uniformity and magnetic interference problems associated with magnetron PVD energy sources.
Co-assigned U.S. Pat. No. 5,630,916 to Gerrish et al. overcomes many of these problems by positioning a plate-shaped electromagnet adjacent to the substrate positioned over a substrate support. The plate-shaped electromagnet is isolated from the processing environment by the substrate support (i.e., electromagnet located outside the vacuum processing chamber) but is still close to the substrate. The substantially planar plate-shape of the electromagnet, which parallels the substrate, produces a uniaxial field of high uniformity and relatively low skew in the immediate vicinity of the substrate surface. An angularly adjustable support provides for mechanically orienting the plate-shaped electromagnet with respect to the substrate support for fine tuning the magnetic orientation axis.
More recently, tolerances for magnetic field skew (angular deviation from the preferred orientation axis) and non-uniformity have become increasingly stringent and the size of the substrates has become increasingly large. Both trends pose similar problems for the available magnetic field orienting equipment. Larger electromagnets can be used to some extent. However, various practical considerations limit the size of the electromagnets. For example, Gerrish et al.""s electromagnet is required to fit within a substrate holder, which is itself limited in size by surrounding vacuum processing chamber dimensions. Unused portions of the magnetic fields produced by the larger magnets beyond the substrate surface area can interfere with substrate processing such as by altering the path of ions to the substrate (thus causing plasma process uniformity degradation) or imbalancing target erosion (e.g., via magnetic field interference with the PVD magnetron energy source).
A reduction in the skew of uniaxial magnetic fields used for orienting thin magnetic films has been achieved by arranging an electromagnet with a specially shaped core and with windings that depart from a common orientation. Preferably, the core of our new electromagnet takes the form of a plate having a peripheral shape that departs from a rectangle in the direction of a circle to contribute to the reduction in skew while economizing space within a chuck housing. The windings are preferably individually spaced and progressively bent to form a pattern that improves uniaxial alignments of the magnetic field and increases the useful area of the magnetic field for orienting thin magnetic films on larger substrates.
Our new electromagnet is preferably mounted in a chuck assembly that supports a substrate for processing in a low-pressure environment. The substrate is supported on a mounting surface of a chuck housing. The electromagnet is supported within an interior space of the chuck housing and produces a substantially uniaxial magnetic field in a plane of the substrate""s surface. The magnetic field provides for magnetically orienting thin films on the substrate""s surface during operations such as plasma sputtering, ion-beam deposition, and thermal annealing.
A magnetically permeable core of the new electromagnet is preferably plate-shaped and has a center, a periphery, and front and back sides wrapped by electrically conductive windings. The core periphery departs from a rectangular shape to achieve performance requirements while more completely filling the interior space of the chuck housing. Front portions of the electrically conductive windings extend across the front side of the plate-shaped core between the front side of the core and the mounting surface of the chuck housing. Back portions of the electrically conductive windings extend across the back side of the plate-shaped core in positions separated from the mounting surface by the core. The front winding portions individually depart from a linear form by differing amounts to reduce skew of the uniaxial magnetic field throughout the plane of the substrate""s surface.
First and second orthogonal axes extend parallel to the front side of the plate-shaped core intersecting at the center of the core. The electromagnetic windings are wrapped around the first orthogonal axis and extend across the front side of the plate-shaped core in a pattern such that (a) the front portions of the windings close to the center of the core extend substantially parallel to the second orthogonal axis and (b) the front portions of the windings spaced from the center of the core are increasingly bowed with respect to the second orthogonal axis for reducing skew of the uniaxial magnetic field along the surface of the substrate.
The bowed winding portions preferably have generally concave shapes facing the center of the core in a pattern that is symmetric with respect to both the first orthogonal axis and the second orthogonal axis. A center section of the individual bowed winding portions extends parallel to the second orthogonal axis and two end sections of the individual bowed winding portions are bent with respect to the second orthogonal axis. The center sections are spaced apart, such as by shims, and the two end sections are spaced more tightly together along the core periphery. The spacing differences between the center and end sections incrementally increases bending at the core periphery as a function distance in either direction along the first orthogonal axis from the core center. Incremental length variations between adjacent center sections of the windings support smooth transitions between the straight center sections and the bent end sections of the windings.
The non-rectangular periphery of the plate-shaped core preferably departs from a rectangular shape in the direction of a circle. The most preferred shape of the core periphery is a circle, which contributes to a reduction in skew and more completely fills the available interior space within the chuck housing.